1. Field of the Invention
The present invention relates to an improvement of a valve mechanism in a slide type exhaust brake system, connectively interposed in an exhaust pipe generally in a large-sized vehicle such as a truck, a bus or the like, for imparting braking effects to the vehicle by creating a load on the machinery while blockading an exhaust passageway of an exhaust gas flowing through the exhaust pipe when travelling on sharp slopes
2. Description of the Prior Art
A valve mechanism in this type of conventional exhaust braking system is, as illustrated in FIG. 6 (see U.S. Pat. No. 4,819,696), arranged such that: a tabular valve member (20) incorporated in a reciprocatory passageway of a housing of a brake body is secured to the top of a piston rod and has its surface formed crosswise with a slot-like exhaust pressure adjusting hole (21); a frame member accommodating a liner member (23) sliding on the surface of valve member (20) which may be conceived as an auxiliary valve member (22) is fitted to a portion in close proximity to the top of piston rod through a block member engaging with valve member (20); the surface of the valve member is formed with an exhaust gas escape hole (24) intended to prevent an excessive load on the machinery when closing the exhaust passageway; when opening and closing the exhaust passageway, the top of the piston rod and the side surface of the block member engage with or impact on valve member (20); and subsequently, liner (23) on the side of auxiliary valve member (22) functions to open and close exhaust pressure adjusting hole (21), thus thrusting the valve member in one direction and pulling up it in the other direction.
Exhaust gas escape hole (24), passing through the surface of valve member (20), for preventing the excessive load has a least hole area within such a range that the machinery does not cease to behave in association with a magnitude of machine output and a braking function. In the foregoing conventional valve mechanism, however, exhaust gas escape hole (24) is formed simply in the surface of valve member (20), and hence, for instance, the exhaust pipe stands erect. Besides, valve member (20) of the exhaust brake system slides in a horizontal direction, and liner member (23) is mounted downwards. In such a state, liner member (23) acts to close the exhaust passageway by its own weight, at which time the exhaust gas is partly discharged from exhaust gas escape hole (24) of valve member (20). In addition, there is created a gap between sliding surfaces of liner member (23) and closed exhaust pressure adjusting hole (21). There is possibility where the exhaust gas escapes from this gap, resulting in an incipient delay in braking and also a loss of braking effects.